Endocrine Abstracts (2008) 16 P44

Quantitative real time RT-PCR of CYP11B2 (aldosterone synthase) to confirm the diagnosis of aldosterone-producing adenomas

Bianca Ueberberg1, Ricarda Althoff1, Timo Deutschbein1, Nicole Unger1, Jakob Hinrichs2, Martin K Walz2, Kurt W Schmid3 & Stephan Petersenn1

1Division of Endocrinology, Medical Center, University of Essen, Essen, Germany; 2Department of Surgery and Center of Minimally Invasive Surgery, Kliniken Essen-Mitte, Essen, Germany; 3Institute of Pathology, University of Essen, Essen, Germany.

Background: The diagnosis of hyperaldosteronism is hindered by the absence of a well-defined gold-standard. CYP11B2 (aldosterone synthase) belongs to the steroid-metabolizing enzymes catalyzing the last step of the aldosterone synthesis. To establish a molecular marker for aldosterone-producing adenomas, we compared the expression in various adrenal tumors.

Methods: Tissue from 20 aldosterone-producing adenomas (APA), 12 hyperplasias associated with hyperaldosteronism (H), 20 cortisol-producing adenomas (CPA), 20 pheochromocytomas (PHEO), and 20 non-functional adenomas (NFA) was obtained following laparoscopic surgery. The diagnosis was confirmed by various biochemical tests, histological investigation, and clinical follow-up. Extracted RNA underwent Real Time RT-PCR using CYP11B2 specific primers and probe (detection limit 5×101 copies/μg RNA (cp)). mRNA levels were normalized to GAPDH mRNA levels. ROC analysis was performed to established cut-offs with specificity of at least 95%.

Results: APA demonstrated high CYP11B2 expression with a median of 1.4×108 cp (range 6.1×105–1.9×1011 cp). In contrast, expression was significantly lower (P<0.001) in CPA, PHEO, and NFA with 5×101 cp (5×101–8.9×106 cp), 4.7×102 cp (5×101–2.3×107 cp), and 5×101 cp (5×101–2.5×106 cp), respectively. ROC analysis suggested a threshold of 1×107 cp with a sensitivity of 90% and specificity of 97%. In H, CYP11B2 expression levels ranged from 5×101 to 2.7×109 with a median of 1.9×105 cp. Inclusion of H to the ROC analysis led to an identical cut-off with lower sensitivity (69%) and similar specificity (97%).

Conclusion: Characterization of CYP11B2 expression may serve as a molecular marker to distinguish aldosterone-producing adenomas and bilateral hyperplasia from other adrenal neoplasms. Such criteria could be used to evaluate biochemical tests for the diagnosis of hyperaldosteronism. Diffuse hyperplasia of both adrenals in H may lead to hyperaldosteronism even in the presence of low expression of CYP11B.

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